Spurious Laboratory Values in Patients With Leukocytosis.
Tony Malek, Leon Chen
PMID 30507663WHAT IT FOUND
In a patient with white blood cells 800,000/mcL, arterial oxygen was 45 mmHg and potassium 9 meq/dL despite 100% pulse oximetry and no expected EKG changes.
These were spurious lab values. The paper suggests bedside pulse oximetry and careful sample handling.
Key findings
01In a patient with white blood cell count 800,000/mcL, the arterial blood gas showed arterial partial oxygen pressure of 45 mmHg while pulse oximetry showed 100% oxygen saturation, a pattern consistent with leukocyte larceny.
02The same patient had serum potassium of 9 meq/dL but no expected electrocardiogram changes and no renal failure or acidosis, which the paper describes as pseudohyperkalemia from fragile white blood cells releasing potassium in vitro.
03The paper lists possible ways to reduce spurious results, including faster processing, cooling the sample, avoiding pneumatic tubes, gentle handling, and point-of-care testing without centrifuge, while noting conflicting evidence for one collection method.
STILL TO COME
How it was doneWhat they foundWhat it means for RNs
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What it does not show
This is one patient, so it cannot show how often leukocyte larceny or pseudohyperkalemia occurs in severe leukocytosis. The paper does not report whether the suggested sample-handling methods prevented harm or changed management in this patient or in a group. The article notes conflicting evidence about using lithium heparin balanced syringes and point-of-care testing without centrifuge. The mechanisms and correlations are described from background discussion, not measured in this case. The patient had chronic myeloid leukemia and was being followed expectantly due to chemotherapy intolerance, so the situation may not apply broadly.
The easy way to misread this
Do not read the arterial blood gas oxygen of 45 mmHg and potassium of 9 meq/dL as proof of true hypoxemia or dangerous hyperkalemia without considering severe leukocytosis. This is one case, and the pulse oximetry was 100%, the electrocardiogram lacked expected hyperkalemia changes, and the paper explains these can be in-vitro artefacts.